Trombiculosis, also known as trombiculiasis，trombidiosis，or trombidiiasis, is a dermatitis caused by trombiculid mites, also known as chiggers.
Chigger adults and nymphs do not suck blood, but feed on the eggs of other animals and plant juices. They like to live in moisty and grassy bushes. Only the larvae suck blood. The larvae parasitize mammals, birds, and reptiles, and amphibians, and sometimes invade humans.
When the host stays in the habitats, the larvae are attracted to the host by the host’s smell. They pierce the skin with cheliceral claws, inject saliva, and absorb the host’s tissue fluid, lymph fluid, and blood. Generally, they do not change their positions or hosts during blood sucking. They can stay in the host for 40 - 72 hours, up to 10 days.
Signs and Symptoms
The bite sites are mostly the calves, waist, posterior hairline, auricle, groin, external genitalia, and anus, followed by the wrist, head, neck, chest, and abdomen. Chigger larva bites can cause not only skin lesions but also tsutsugamushi fever, also known as tsutsugamushi or scrub typhus, caused by rickettsiae carried by the larvae.
Figure 1 skin lesions
There are non-itchy red papules or wheals initially on the bite sites, with a small petechia or pustule on the top, gradually increasing to pea sized. The rashes are necrotic and crusted in 1 - 2 days, evolving to eschars, with red halos. There are small ulcers under the crusts but not pus. There are enlarged neighboring lymph nodes and tenderness. Patients may suddenly develop high fever, chills, dizziness, nausea, muscle aches, fatigue, and drowsiness in 1 - 2 weeks.
Figure 2 eschar
On the basis of the typical clinical manifestations, particularly eschars, the condition can be diagnosed.
Topical 5% sulfur cream or 1% phenol calamine lotion are appropriate. Antihistamines are given to patients with severe symptoms. Tsutsugamushi with systemic symptoms can be treated by chloramphenicol, tetracycline, or chlortetracycline.